Things working FOR you: 3GHz, 1TB HD, 20" monitor, cool looking case (?) and a Windows 7 license.
Things working AGAINST you: The LGA775 platform has very little bang-for-the-buck upgrades. 2GB of memory. "Dated" video card. Small power supply ??
IMHO your target audience is someone that "just needs a computer that works" and you should expect to MAYBE get enough from it to cover the cost of a new CPU+MB if you are planning a new build. Few knowledgeable people would buy a similar machine to be upgraded for gaming or processing efforts. Prices are subjective so not going to gustimate there... Good luck!